Bulky quantum dots exhibit unique optical/electrical properties which no semiconducting materials shows. Due to these unique properties, nano quantum dots are becoming of central interest as a material for next-generation high-brightness LEDs, biosensors, lasers, solar cells, etc.
Conventionally, quantum dots have been produced mainly in laboratories in such a way to quickly inject cooled precursors into a high-temperature solvent to create nucleuses and then grow the nucleuses under the appropriate temperature conditions. However, the conventional method has limitations in respect to mass production of quantum dots, since it has poor reaction control to make the particle sizes non-uniform and cause great loss in subsequent processes due to reaction conditions depending on the amount of particles, which severely reduces the production amount. Particularly, in the case of quantum dots, the particle size has a direct influence on the optical/electrical properties, uniformity in particle diameter is linked directly with the quality of quantum dots and if the non-uniformity exceeds a predetermined limit, the quantum dots lose their unique qualities and become commercially worthless.
U.S. Pat. No. 6,682,596 discloses a method of combining reactants with a solvent to form a solution and continuously passing the solution at a selected flow rate through a thermally conductive tube that is maintained at a temperature sufficiently high, thereby producing a product mixture containing nanocrystals. This method exhibits excellent uniformity in diameter upon low-volume production, but still has a limitation that it is difficult to be applied to mass-production due to non-uniform mixing through a narrow tube.
Technical Problem
The present invention provides an apparatus and method for mass production of quantum dots.
The present invention also provides an apparatus and method for mass-producing quantum dots with uniform particle diameters at high yield.
Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention.
Technical Solution
According to an exemplary aspect, there is provided a quantum dot producing apparatus including a micro mixer in which a plurality of precursor solutions are mixed in such a manner that a plurality of paths diverge from each of a plurality of input ports to which the precursor solutions are respectively supplied, the diverging paths joining with other paths diverging from the other one of the input ports, and then the joined paths are collected into an output port.
A mixing ratio of precursors influences a particle diameter. When precursor solutions are abruptly mixed, the mixing ratio of precursors varies locally to cause irregular reactions, which leads to non-uniformity of particle diameters. The non-uniform mixing is one of reasons why conventional quantum dot producing methods including the U.S. Pat. No. 6,682,596 have failed to mass-produce quantum dots.
Meanwhile, the mixer according to the present invention mixes precursor solutions flowing therethrough very uniformly over the entire area, which leads to uniform nucleation. The mixer solves the problem that the U.S. Pat. No. 6,682,596 has failed to mass-produce quantum dots since the wider a tube diameter, the more difficult uniform mixing. The mixer adopts a method similar to mixing thorough several dozens or hundreds of tubes each having a size similar to that adopted in the U.S. Pat. No. 6,682,596. Accordingly, the mixer according to the present invention achieves mass-production of quantum dots.
As described above, according to the present invention, by diverging each of a plurality of precursor solutions into micro streams, joining the diverging micro streams in pairs with each other and then collecting the joining streams, the precursor solutions can be mixed at a constant rate, which leads to mass-production of quantum dots.
According to another embodiment, the mixer of mixing the precursor solutions is heated. In this case, the heating temperature may be a temperature at which quantum dots are created.
Even when the mixer remains at room temperature, some quantum dot nucleuses are created during the process of mixing the precursor solutions. These unintended quantum dot nucleuses have an adverse effect upon uniformity of particle diameter. In the current embodiment, the mixer is disposed inside a heating furnace so as to perform nucleation uniformly in a short time, thereby further improving uniformity of particle diameter.
According to another exemplary embodiment, the quantum dot producing apparatus further includes a buffer which is disposed between the mixer that is heated and a heating furnace and which passes a precursor mixture at a relatively low temperature.
The buffer functions to stop the process of quantum dot nucleation such that the process of nucleation is more completely separated from the process of nuclear growth, which further improves uniformity in particle size of quantum dots.
According to another exemplary embodiment, the quantum dot producing apparatus heats the precursor mixture solution through a first heating part that is heated to a first temperature and then sequentially heats through a second heating part that is heated to a second temperature lower than the first temperature.
In the case of a quantum dot producing apparatus utilizing a single heating furnace, nucleation and nuclear growth may occur simultaneously or inconstantly, thus resulting in creation of different sizes of quantum dot nucleuses.
In general, a temperature range for nucleation of quantum dots partially overlaps a temperature range for nuclear growth, but the temperature range for nucleation is relatively higher than the temperature range for nuclear growth. In the current embodiment, nucleation is separated from nuclear growth to an appropriate degree by separately providing a first temperature condition under which nucleation occurs and a second temperature condition under which nuclear growth occurs, which leads to uniformity improvement of particle size.
The quantum dot producing apparatus according to the current embodiment further includes a buffer disposed between the first heating furnace and the second heating furnace, and passing a solution through the buffer which is at a third temperature that is lower than the first and second temperatures.
The buffer functions to stop the process of quantum dot nucleation such that the process of nucleation is more completely separated from the process of nuclear growth, which further improves uniformity in particle size of quantum dots.
Advantageous Effects
As described above, according to the present invention, by mixing precursor solutions in such a manner as to diverge each precursor solution into micro streams, mix the diverging micro streams in pairs and then collect the mixture, a large amount of solutions can be mixed uniformly like when a small amount of solutions is mixed, thereby achieving mass-production of quantum dots.
Also, by separating a process of nucleating quantum dots from a process of growing quantum dot nucleuses, quantum dots with uniform particle diameters can be produced at high yield.